This invention relates to improved surface-treated charge control agent compositions, and a process for producing such compositions. The process is particularly useful in the production of charge control agents and other external additives for use in electrophotographic toner and developer compositions. The present invention also relates to such surface-treated charge control agent compositions produced by an adsorption process.
The surface-treated charge control agent compositions produced by the adsorption process may be utilized for making electrophotographic toners and developers according to conventional methods. Such toners and developers may then be used in conventional electrophotographic imaging processes.
Combinations of charge control agents and flow aid particles and methods for producing such combinations are known in the art.
Charge control agents may be produced and coated onto flow aid particles by a variety of different methods. Such methods include solution coating and vapor phase reaction.
For example, U.S. Pat. Nos. 5,256,514, 5,256,515 and 5,300,389, all to Law et al., the disclosures of which are incorporated herein by reference, disclose halogenated salicylic acid charge enhancing additives. The disclosed charge enhancing additives may be incorporated into the toner or the additives may be present on the toner surface or coated onto toner additives such as colloidal silica. Where the charge enhancing additives are coated onto toner additives such as colloidal silica, such coating is conducted using the conventional solution coating or vapor phase reaction processes. Toner compositions incorporating the disclosed charge enhancing additives may be triboelectrically charged to a value of between -10 and -50 .mu.C/g.
U.S. Pat. No. 4,734,350 to Lin et al. discloses modified charge enhancing additives which are chemically bonded to or chemisorbed onto flow aid particles such as silica particles. In one embodiment, an amine or amino alcohol is reacted with the flow aid particles by heating a solution of the components. In another embodiment, the charge additive is prepared by a series of reactions between the flow aid particles with a silylating material and an amine. These processes are, however, different from the adsorption process of the present invention. Lin discloses that the charge enhancing additives are themselves chemically modified, and are chemically bonded to or chemisorbed onto the surface of the flow aid particles. By chemisorbed is meant that the charge enhancing additive participates in a chemical interaction with the flow aid particle. Thus chemical bonding and chemisorption (or chemical adsorption) are distinct from the adsorption of the present invention, wherein the charge enhancing additive is adhered to the surface of the flow aid particles by a relatively small attractive force, such as by van der Waals forces, rather than by being chemically altered and attached to the flow aid particles.
The focus in the toner/developer community has been to coat charge control agents onto flow aid particles using a solution coating process followed by a fluidized bed spray drying process to produce homogeneous or inhomogeneous mixtures of the charge control agent and the flow aid particles. This process is effective in producing good quality charge control agents, and can be scaled up for industrial applications. A problem with such conventional processes is that they produce charge control agents that possess several disadvantageous properties. Specifically, the admix time for such conventional charge control agents may be lengthy, and the triboelectric charging characteristics of the particles are not as high as would be desired for toner and developer applications.